What's the problem with the @GetHTTPHeader? It is working for me in the beta 4.

To make the hidewhen formulas work in view actions, you will need to change the xsl in the DXLExporter agent, so that the formulas are returned and handle them in the code of Ext.nd.Actionbar.
I started that task once but haven't finished it due to other commitments and also because I didn't need the hidewhen's yet.